The present invention relates to valves for restricting fluid flow and, in particular, to valves which restrict a fluid flow to flow in a conduit in a single direction, such as check valves.
Varieties of valve means are known and have been suggested for restricting fluid flow in a conduit or from one conduit, in which the valve means is integrated, into another conduit or chamber (hereinafter solely "conduit"). Valves which restrict flow in a single direction are known commonly as check valves, such valves being positioned in a conduit to provide for sealing off and opening the conduit to fluid flow. In general, check valves are categorized by their structure, thusly being known as, for example, gate valves, ball valves and spring-loaded valves. Such valves may be employed usefully, for example, in systems for filling and emptying fluids, an example being illustrated in U.S. Pat. No. 4,375,864, which employs a gate valve, and it is known that Wenget extruder apparati include a ball valve for injecting steam into a barrel of an extruder for heating a substance mix and for load control. Spring-loaded valves may be employed usefully in systems wherein a substance, which is not in a state which interferes spring operation, is introduced from a conduit into a reaction vessel.
Generally common to the check valve assemblies noted above is that if or when such valves are integrated into a system to supply fluid from a first conduit to a second conduit in which a fluid substance different from that restricted by the valve flows, the valve seat and the seal are exposed to the different fluid substance when it flows through the second conduit. One consideration which arises, therefore, in a two-fluid two-conduit system is the potential of seal failure, which can result at least in contamination of the valve, if not, the flow passage of the first conduit, itself, with respect to which the valve is integrated.
Additionally, although check valve assemblies integrated in a first conduit of a two-conduit two-fluid system generally function acceptably when the substance flow in the second conduit is intermittent and alternates with the flow restricted by and introduced into the second conduit by the valve, the potential for problems increases in the case when a fluid from the first conduit is introduced via the valve into the second conduit while a different substance is flowing in the second conduit. In such cases, when the valve is open for fluid flow, the substance flowing in the second conduit may be afforded access to the seat and the seal, which can result in fouling the seat and the seal which, in turn, inhibits effective seating and hence, sealing upon closing the valve to fluid flow, and this can be particularly problematical if the substance which flows in the second conduit is a viscous and/or tacky substance.